In the recent years, an organic light emitting diode (OLED), also known as an organic electroluminescence display, has become a main display type of flexible displays due to its various advantages.
A flexible OLED display has a high demand on the uniformity and the reliability of a threshold voltage (Vth) of a thin film transistor (TFT), i.e., an electrical bias threshold voltage drift (bias stress) characteristic. Generally, it is required that the drift of the threshold voltage (ΔVth) is less than 0.3V. Therefore, a control of electrical bias threshold voltage drift and a structure improvement/a process improvement of the flexible thin film transistor and the like have become the technology development trend of flexible TFT-driven OLED displays.
A self-heating effect is a major cause of the electrical bias threshold voltage drift generated by the thin film transistor. For a thin film transistor of a high resolution and a short channel, the self-heating effect is more obvious, and the maximum leakage currents (Ids) of the thin film transistor may be four to five times larger than the minimum Ids due to the self-heating effect.
How to avoid the self-heating effect is one of the technical problems to be solved in the art.